A ten-year birch pollen record for Reykjavik, Iceland, has been analyzed with respect to fluctuations in the annual pollen sum, the starting date, and the duration of the birch pollen season. A three-year cycle is observed for the annual birch pollen sum, which could be of value in predicting the severity of the next birch pollen season. The annual birch pollen sum is regressed on six climatic variables, only one of which turned out to be statistically significant. The number of days with temperatures above +7.5°C in the year of inflorescence initiation shows a significant correlation with the annual birch pollen sum of the following flowering year (P =0.009). For the starting date of the birch pollen season the accumulated thermal sum on May 15 is shown to have the best predictive value, estimating it to within one week. The mean duration of the birch pollen season in southwestern Iceland is 17 days, starting May 29 and ending June 14.
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